MulticalcPipe Flow Rate Calculator
Calculate flow rate and velocity for circular pipesEnter pipe parameters to calculate flow.
Pipe Flow Guide
Understanding Pipe Flow
Pipe flow calculations are based on the continuity equation, which relates flow rate, cross-sectional area, and velocity.
Key Formulas:
- Flow Rate: Q = A × V
- Velocity: V = Q / A
- Area (Circular): A = π × (d/2)²
- Q = Flow rate, A = Cross-sectional area, V = Velocity, d = Diameter
Typical Flow Velocities:
- Water (gravity): 0.5-1.5 m/s (1.6-5 ft/s)
- Water (pumped): 1-3 m/s (3-10 ft/s)
- Steam: 15-30 m/s (50-100 ft/s)
- Air (HVAC): 5-10 m/s (16-33 ft/s)
Common Pipe Sizes:
- Residential water: 15-25 mm (½"-1")
- Commercial water: 50-100 mm (2"-4")
- Fire sprinkler: 25-100 mm (1"-4")
- HVAC ductwork: 100-600 mm (4"-24")
Applications
- Plumbing: Water supply sizing
- HVAC: Duct and pipe design
- Fire Protection: Sprinkler system design
- Industrial: Process piping
Pro Tips
-
Velocity
Limits
Too fast = noise & erosion. Too slow = sediment buildup. Aim for 1-3 m/s for water. -
Diameter Matters
Doubling diameter quadruples area and flow capacity (at same velocity). -
Pressure Drop
This calculator doesn't account for friction losses. Use Darcy-Weisbach for pressure drop.
Example
100mm diameter pipe:
- d = 100 mm = 0.1 m
- A = π×(0.05)² = 0.00785 m²
- V = 2 m/s
- Q = 0.00785 × 2 = 0.0157 m³/s
- Q = 942 L/min ≈ 249 GPM
Frequently Asked Questions
A: Use the continuity equation: Q = A × V, where Q is flow rate, A is cross-sectional area (π×(d/2)² for circular pipes), and V is velocity. For example, a 100mm pipe with 2 m/s velocity: A = 0.00785 m², Q = 0.0157 m³/s = 942 L/min.
A: For water systems, aim for 1-3 m/s (3-10 ft/s). Below 0.5 m/s risks sediment buildup. Above 3 m/s causes noise, erosion, and water hammer. Gravity systems: 0.5-1.5 m/s. Pumped systems: 1-3 m/s. Fire protection: up to 6 m/s.
A: No, this calculator uses the continuity equation (Q = A × V) which doesn't include friction losses. For pressure drop calculations, use the Darcy-Weisbach equation or Hazen-Williams formula, which account for pipe roughness, length, fittings, and fluid properties.
A: Flow rate is proportional to area, which is proportional to diameter squared. Doubling the diameter quadruples the area and flow capacity (at the same velocity). For example, a 2" pipe has 4× the capacity of a 1" pipe at the same velocity.
A: Always use the actual internal diameter (ID), not nominal size. For example, a "1-inch" Schedule 40 steel pipe has an ID of about 26.6mm (1.049"), not 25.4mm (1"). Check pipe specifications for exact ID. Our calculator uses the diameter you input.
A: The continuity equation (Q = A × V) applies to both liquids and gases. However, for compressible gases at high velocities or pressure changes, you need compressible flow equations. This calculator is most accurate for incompressible fluids (liquids) or low-velocity gases.
Disclaimer
Important Notice:
- This calculator uses the continuity equation (Q = A × V) which assumes steady, incompressible flow in circular pipes.
- Calculations assume uniform velocity across the pipe cross-section. Actual velocity profiles vary (laminar vs turbulent flow).
- This tool does NOT calculate pressure drop. Friction losses, elevation changes, and fittings cause pressure drop not shown here.
- For compressible gases at high velocities or significant pressure changes, use compressible flow equations.
- Pipe diameter should be the actual internal diameter (ID), not nominal size. Check pipe specifications.
- Flow velocities have practical limits: too fast causes erosion and noise, too slow causes sediment buildup. Follow industry standards.
- For system design, consider: pressure requirements, elevation changes, pipe roughness, fittings, valves, and safety factors.
- This calculator is for preliminary design and education. For final plumbing, HVAC, or fire protection design, consult licensed professionals.
- Building codes have specific requirements for pipe sizing, materials, and velocities. Always follow applicable codes.
- We are not responsible for any errors, system failures, code violations, or other consequences resulting from the use of this calculator.
Always verify calculations with qualified professionals and follow applicable plumbing and building codes.
Pipe Flow Calculator
Calculate flow rate from velocity or velocity from flow rate. Perfect for plumbing, HVAC, and piping design!
Calculator Modes
Calculate flow rate (Q) from pipe diameter and fluid velocity using Q = A × V
Calculate velocity (V) from pipe diameter and flow rate using V = Q / A
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Did You Know?
The world's largest water pipe is the California Aqueduct, with sections up to 12 meters (40 feet) in diameter, carrying water over 700 km!